1. Field of the Invention
This invention relates to a throttle control system for automotive internal combustion engines, more particularly to a system for controlling opening of a throttle valve of automotive internal combustion engines in which the throttle valve is not only mechanically linked with the accelerator pedal but also connected with an actuator so as to be openable and closable thereby, and still more particularly to such a system which prevents deterioration in accelerator pedal feeling caused by change in the amount of accelerator pedal depression force required when the actuator is in operation, namely eliminates any unnatural or unpleasant feeling the operator might otherwise experience because of change in the amount of foot pressure required to depress the accelerator pedal.
2. Description of the Prior Art
In most automobiles and other vehicles powered by internal combustion engines, the throttle valve of the internal combustion engine is mechanically linked with an accelerator pedal so that the operator can open and close the throttle valve by varying the amount of depression of the accelerator pedal. However, there has recently been proposed another arrangement wherein an actuator, e.g. a motor, linked with the throttle valve drives the throttle valve in the required direction according to the amount of accelerator pedal depression detected. A system of this type is disclosed, for example, in Japanese Laid-open Patent Application No. 59(1984)-99045.
There are also known systems that combine the arrangements just mentioned. In these, in addition to the throttle valve being mechanically linked to the accelerator pedal, it is also connected with an actuator, and the throttle valve is opened and closed by both the accelerator pedal and the actuator. An example of such a system is shown in FIG. 7. In the illustrated arrangement, the throttle valve is linked both with the accelerator pedal, mechanically by a wire or the like, and with a pulse motor such that after the throttle valve has been opened by a certain amount by the action of the accelerator pedal, the degree of opening can be finely adjusted by the closing action of the pulse motor. This is advantageous in that it enables the throttle valve to zero in on an optimum degree of opening for, by way of example, realizing optimum fuel economy.
To be more specific, the throttle valve 12 provided in an air intake passage 10 is fixed to a throttle valve shaft 14 so that the air intake passage can be opened and closed by rotation of the shaft 14, thereby adjusting the amount of intake air in the known manner. A portion of the throttle valve shaft 14 extends to the exterior of the air intake passage 10 at either side thereof and a throttle drum 16 is fit on the external portion on one side through a collar so as to be free to rotate thereon. The throttle drum 16 is mechanically linked with an accelerator pedal 22 via a wire 18 and a linkage mechanism 20 in such manner that when the operator depresses the accelerator pedal 22, the throttle drum 16 rotates in the direction of the arrow a, i.e. counterclockwise as seen in the figure. The shaft 14 further has a throttle lever 24 rigidly fixed thereon adjacent to the throttle drum 16 and a lost motion spring 26 is mounted between the throttle drum 16 and the throttle lever 24. When the throttle drum 16 is rotated counterclockwise, i.e. in the direction of arrow a, owing to depression of the accelerator pedal 22, the spring 26 causes the throttle lever 24 to follow this motion, i.e. to rotate in the same direction up to the point that a bar 24b extending laterally from an arm 24a of the throttle lever 24 abuts against an arm 16a of the throttle drum 16. This rotation of the throttle lever 24 is transferred to the throttle valve shaft 14 and causes the throttle valve 12 to open. In addition, a return spring 28 is mounted on the shaft 14 between the throttle lever 24 and a projection 10a on the air intake passage 10, which urges the throttle valve 12 in the closing direction. The return spring 28 is provided as a fail safe means in a case when no force acts on the throttle valve or the throttle valve shaft.
The end of the shaft 14 outward from the throttle drum 16 has a throttle valve closing lever 30 mounted thereon via a collar 32 so as to be freely rotatable with respect to the shaft 14. When the throttle valve closing lever 30 rotates clockwise as indicated by the arrow b, a bar 30b extending laterally from an arm 30a thereof engages with a second bar 24d extending laterally from a second arm 24c of the throttle lever 24, causing the throttle lever 24 to rotate clockwise as indicated by the arrow c and thereby closing the throttle valve 12. The throttle valve closing lever 30 has a second arm 30c, extending to the opposite direction to the first arm 30a, which is linked via a connection rod 34 to one end of a boomerang-shaped lever 40 attached to the drive shaft 38 of a pulse motor 36. When the pulse motor 36 rotates in the forward and reverse directions between the positions at which the motor lever 40 abuts against a stop 42, the throttle valve closing lever 30 is rotated in one direction or the other accordingly. For example, when the connection rod 34 is moved in the direction of the arrow d, the throttle valve closing lever 30 rotates in the direction of the arrow b. The pulse motor 36 is controlled by a control unit 50 which computes a control value based on signals received from a throttle opening sensor 52 which is disposed on the portion of the shaft 14 extending on the other side of the air intake passage 10 and detects the degree of opening of the throttle valve 12, from an accelerator pedal depression sensor 54 located in the vicinity of the accelerator pedal 22 for detecting the amount of depression of the accelerator pedal, an intake air pressure sensor 56 disposed at an appropriate location within the air intake passage 10 downstream of the throttle valve 12 for detecting the pressure in the air intake passage as an absolute value, and a crankshaft angle sensor 58 located in the vicinity of a rotating member, not shown, of the internal combustion engine for detecting the angular position of the engine crankshaft. The computed control value is used to control the operation of the pulse motor 36.
In the arrangement shown in FIG. 7, the torque acting on the throttle valve shaft 14 is required to be: EQU M&gt;L-B&gt;C
wherein M is the torque produced by the pulse motor 36, L is the maximum torque of the lost motion spring 26, B is the maximum torque of the return spring 28 and C is a constant. In the formula, if the constant C is set too low, the throttle valve will be incapable of properly assuming the fully opened state, whereas if it is set too high, the accelerator pedal feeling will be degraded. The constant should therefore be determined appropriately. Moreover, regardless of the value at which it is set, it is clear from the foregoing relationship that the valve closing force B of the return spring 28 has to be larger than the constant and that the force L of the lost motion spring 26 must be greater than the return spring force such that the lost motion spring can cause the throttle lever 24 to follow the counterclockwise rotation of the throttle drum 16 thereby opening the throttle valve 12.
Thus, the throttle valve 12 is urged in the closing direction by the return spring 28 and the force of this spring 28 is transmitted through the lost motion spring 26, the wire 18, etc. to the accelerator pedal 22 where it constantly acts as a force opposite to the pedal depression force applied by the operator. In the prior art system, therefore, once the accelerator pedal 22 has been depressed to cause the throttle drum 16 to rotate counterclockwise as indicated by the arrow a and the throttle lever 24 follows this rotation under the force of the lost motion spring 26 thus opening the throttle valve 12, if the pulse motor 36 then rotates in the forward direction so that the connection rod 34 is moved in the direction of the arrow d, the throttle valve closing lever 30 is rotated clockwise as indicated by the arrow b, the throttle lever 24 is rotated clockwise as indicated by the arrow c counter to the force of the spring 26 by force received via the bar 30b and the bar 24d engaged, and the throttle valve 12 is thus rotated in the closing direction, the result will be that the force of the spring 26 will be added to that of the return spring 28, causing the amount of force required to depress the accelerator pedal 22 to change stepwise as shown in FIG. 8 and this will degrade the accelerator pedal feeling and cause the operator to experience an unnatural or uncomfortable sensation. It should be noted that the force of the return spring 28 for urging the throttle valve 12 in the closing direction is required to be relatively large and the force of the spring 26 has to be even larger in order to be able to overcome its force and open the throttle valve as stated before with reference to the formula. Thus, combined force of the two springs, which causes intermittent variation in the required amount of accelerator pedal depression force, is too large to be ignored.